This invention relates to a starting device for use in a direct-injection internal combustion engine (hereinafter, xe2x80x9cenginexe2x80x9d), wherein fuel is injected into combustion chambers directly.
In recent years, to achieve reductions in emissions and improvements in fuel economy, direct-injection engines, wherein fuel is injected directly into combustion chambers, have been brought to use. This kind of engine is constructed such that it is possible to switch between a uniform combustion, wherein fuel is injected during the intake stroke to create a uniform mixture in the combustion chamber, and a stratified combustion, wherein fuel is injected during the compression stroke to create a stratified mixture. In the stratified combustion, after a mixture close to a theoretical air/fuel ratio is created around a spark plug, an extremely lean mixture is realized in the combustion chamber as a whole. The stratified combustion is generally limited to low-speed, low-load operating regions; however, in an engine disclosed in Japanese Unexamined Patent Publication No. H.10-30468, when the engine temperature is above a set temperature and the fuel pressure is above a set pressure, a stratified combustion is effected with a compression stroke injection from the time of starting.
In the engine disclosed in the above-mentioned publication, the object of effecting the stratified combustion from starting is to obtain the emissions and fuel economy benefits of the stratified combustion from the time of starting. Accordingly, the control procedure for starting is the same as in an ordinary engine. In this control procedure, first, a cylinder identification is carried out at the commencement of cranking, and when, after the completion of this cylinder identification, a cylinder reaches its compression stroke, a fuel injection into this cylinder is executed with a predetermined injection quantity and a predetermined injection timing.
That is, in the engine of the above-mentioned publication, no consideration is given to shortening of the time required for starting, and it is not possible to satisfy a desire to shorten the starting time. Delay in engine starting is a problem even in an ordinary vehicle, but particularly in hybrid vehicles and idle-stop vehicles which have come into use in recent years, there is the problem that when there is a delay in starting, it is impossible to exploit their advantages fully. For example, in a hybrid vehicle, which uses both a motor and an engine as drive sources, starts the engine to obtain output (for example when accelerating from low-load travel under motor drive), any delay in starting the engine causes the output to fall temporarily and reduces acceleration responsiveness. In an idle-stop vehicle, wherein the engine is automatically stopped when the vehicle halts at a stop signal of a traffic signal at a road junction or a pedestrian crossing (hereinafter, referred to as halting at a traffic signal or the like), the problem arises that an engine starting delay leads directly to a delay in starting of the vehicle.
Also, depending on the running state of the engine, progress of a precursor reaction, undergone by fuel injected into a cylinder during the compression stroke, may cause the combustion rate following a spark-firing to become rapid, or may progress the precursor reaction and give rise to a self-ignition before a spark-ignition for the injected fuel. Here, the precursor reaction refers to a phenomenon of hydrocarbons in a fuel decomposing under heat and undergoing a low-temperature oxidation reaction. In this low-temperature oxidation reaction, unlike in combustion ensuing from spark-firing or high temperature combustion, such as combustion caused by flame propagation, fuel combusts gently at a low temperature. If a precursor reaction proceeds, without spark-firing and throughout the combustion chamber, many flame nuclei arise substantially simultaneously and cause self-ignition.
Under these circumstances, trouble such as an increase in engine vibration, the occurrence of knocking, or carbon getting into the injection port of a fuel injection valve exposed in the combustion chamber arises.
It is therefore an object of the present invention to provide a starting device for a direct-injection internal combustion engine with which starting can be completed swiftly.
It is another object of the present invention to provide a starting device for a direct-injection internal combustion engine with which starting can be completed swiftly and also trouble caused by a self-ignition and sudden combustion can be prevented by normal spark-ignition being carried out reliably upon starting.
To achieve these and other objects, in a first preferred embodiment of the invention, a starting device for a direct-injection internal combustion engine, wherein fuel can be injected into cylinders directly, has a cylinder identifying means for performing cylinder identification of the internal combustion engine while the internal combustion engine is stopped; start request determining means for determining whether there is an engine start request of the internal combustion engine; and start control means for injecting fuel into a cylinder in a compression stroke identified by the cylinder identifying means when it is determined by the start request determining means that there is an engine start request of the internal combustion engine.
Accordingly, in a starting device for a direct-injection internal combustion engine of the invention pertaining to this invention, starting of the engine can be completed swiftly because when cranking is commenced for starting, fuel is immediately injected into the cylinder positioned in its compression stroke, and thus a subsequent spark-firing a first combustion is effected quickly.
In another mode of the present invention, the starting device for a direct-injection internal combustion engine has engine temperature detecting means for detecting an engine temperature of the internal combustion engine; piston position detecting means for detecting the position of a piston in the identified compression stroke cylinder; and ignition region determining means for determining, on the basis of the engine temperature detected by the engine temperature detecting means and the piston position detected by the piston position detecting means, whether or not fuel injected into the identified cylinder in the compression stroke will be in an ignition region.
By this means, it is possible to swiftly complete the start of the engine while preventing an ignition failure because injection of fuel into a cylinder in a compression stroke is carried out after determining whether or not fuel injected into the identified cylinder in a compression stroke will be in an ignition region based on the engine temperature and the piston position of the cylinder in the compression stroke by the cylinder identifying means.
In another mode of the present invention, the starting device for a direct-injection internal combustion engine has piston position correcting means for moving the position of the piston of either the identified cylinder in a compression stroke or the cylinder to enter its compression stroke next after the identified cylinder in the compression stroke so that the position of the piston becomes such that fuel injected into the cylinder will be in an ignition region when it is determined that the piston position detected by the piston position detecting means is such that fuel injected into the identified cylinder in the compression stroke will not be in an ignition region. Because by this means, it is possible for the position of the piston to be moved so that injected fuel will be in an ignition region, through fuel injection to a cylinder positioned in its compression stroke being carried out immediately at that time, by a subsequent spark-firing a first combustion can be effected quickly and starting completed swiftly.
To achieve the above-mentioned object and other objects, in the second form of the present invention, a starting device for a direct-injection internal combustion engine has cylinder identifying means for performing cylinder identification of the internal combustion engine while the internal combustion engine is stopped; piston position detecting means for detecting a position of a piston in a cylinder identified by the cylinder identifying means; start request determining means for determining whether or not there is an engine start request of the internal combustion engine; combustion parameter setting means for setting a fuel injection quantity and a fuel injection timing in correspondence with the piston position detected by the piston position detecting means to suppress abnormal combustion of the injected fuel; and start control means for controlling fuel injection for the identified cylinder on the basis of the fuel injection quantity and the fuel injection timing set by the combustion parameter setting means when it is determined by the start request determining means that there is an engine start request of the internal combustion engine.
Accordingly, in a starting device for a direct-injection internal combustion engine of the above invention, as a result of the provision of the construction described above, a fuel injection quantity and a fuel injection timing are set to suppress abnormal combustion of the injected fuel. Therefore, starting of the engine can be completed swiftly because when cranking is commenced for starting, fuel injection is carried out immediately into the identified cylinder at that time, and thus a subsequent spark-firing a first combustion is effected quickly. That is, with this invention, it is possible to swiftly complete the start and fuel can be combusted surely by spark-firing on starting. Therefore, it is possible to prevent trouble caused by a self-ignition and sudden combustion (for example, an increase in engine vibration, occurrence of knocking, or carbon getting into the injection port of a fuel injection valve).
In another mode of the second form of the present invention, the combustion parameter setting means sets the fuel injection quantity further to the increase side as the piston position, before starting of the internal combustion engine, is closer to bottom dead center. This is because, in a cylinder stopped in its compression stroke, as the piston position is closer to bottom dead center, the pressure rise of when the piston moves toward top dead center becomes greater, and thus the self-ignition or sudden combustion is more likely to occur. For a cylinder stopped in its intake stroke, as the piston position is closer to bottom dead center, the amount of residual gas in the cylinder is greater, the amount of fuel from the intake port is less, and thus it is more likely that a self-ignition occurs. Because the fuel injection quantity is increased to match these tendencies, the temperature in the cylinder is lowered by heat of vaporization of fuel. Therefore, starting can be completed swiftly, and trouble caused by the self-ignition and sudden combustion of the kind described above can be prevented by normal spark-ignition being carried out reliably upon starting.
In another mode of the second form of the present invention, the combustion parameter setting means sets an ignition timing to suppress an abnormal combustion of the injected fuel, and the start control means, when it is determined by the start request determining means that there is an engine start request of the internal combustion engine, controls fuel injection for the identified cylinder on the basis of the fuel injection quantity and the fuel injection timing set by the combustion parameter setting means and then controls ignition for the injected fuel into the identified cylinder on the basis of the ignition timing set by the combustion parameter setting means. In this mode, the combustion parameter setting means preferably sets the ignition timing more to the retard side as the piston position, before starting of the internal combustion engine, is closer to bottom dead center.
By this means in this mode, by the ignition timing being set more to the retard side the closer the piston position is to bottom dead center, trouble caused by self-ignition and sudden combustion of the kind described above can be prevented more reliably. For example, for a cylinder stopped in its compression stroke, as the piston position is closer to bottom dead center the pressure rise of when the piston moves toward top dead center is greater, and thus the combustion rate (the combustion speed with respect to crank angle) is more rapid. For a cylinder in its intake stroke, as the piston position is closer to bottom dead center, the amount of residual gas in the cylinder is greater and the amount of intake air from the intake port is less, and thus the temperature in the cylinder during compression is higher and the combustion speed is more rapid. Because the ignition timing is retarded to match these tendencies, the pressure in the cylinder, after ignition is lowered and the combustion rate is suppressed.
In another mode of the second form of the present invention, there are provided engine temperature detecting means for detecting an engine temperature of the internal combustion engine, and the combustion parameter setting means sets a basic fuel injection quantity and a basic fuel injection timing in correspondence with the piston position detected by the piston position detecting means and the engine temperature detected by the engine temperature detecting means, and the combustion parameter setting means corrects at least one of the combustion parameters that are the set basic fuel injection quantity and the set basic fuel injection timing for the identified cylinder in correspondence with the piston position detected by the piston position detecting means to suppress abnormal combustion of the injected fuel. Also, in this mode, the combustion parameter setting means sets a basic ignition timing for the injected fuel into the identified cylinder in correspondence with the piston position detected by the piston position detecting means and the engine temperature detected by the engine temperature detecting means, and the combustion parameter setting means corrects the combustion parameter that is the set basic ignition timing in correspondence with the piston position detected by the piston position detecting means to suppress abnormal combustion of the injected fuel.
In the starting device for a direct-injection internal combustion engine of the second form of the present, as a result of the provision of the construction described above, at least one of the combustion parameters that are the basic fuel injection quantity and the basic fuel injection timing set by the combustion parameter setting means is corrected in correspondence with the piston position detected by the piston position detecting means to suppress abnormal combustion of the injected fuel. Therefore, when cranking is commenced for starting, the starting can be completed swiftly because fuel injection to the cylinder, into which fuel should be injected, is executed immediately at that time, and thus a subsequent spark-firing a first combustion is effected quickly. That is, with this invention, because it is possible for starting to be completed swiftly and fuel can be made to combust reliably by spark-firing upon starting while an abnormal combustion being suppressed, it is possible to prevent trouble caused by self-ignition and sudden combustion.